Biological indicators are used to determine the efficacy of methods of sterilizing articles. Biological indicators contain specific amounts of microorganisms and are designed to be placed within a sterilization device to determine whether such device is operating properly. In this respect, after a sterilization process, the biological indicators are removed and assayed to determine whether a sufficient reduction in the number of microorganisms has taken place. The “D” value of a sterilant is defined as the time increment necessary for one log reduction in bio-burden.
Biological Indicator Evaluator Resistometers (BIER's) have been developed to test such biological indicators. Basically, a biological indicator is placed within a BIER vessel and a sterilization cycle is run to expose the biological indicator to a sterilant for a predetermined period of time. Ideally, the biological indicator is exposed to a predetermined concentration of sterilant for a predetermined exposure time. However, in most BIER systems, there are “transient” periods preceding and following the desired exposure time, as the concentration of the sterilant within the vessel builds up (typically from a zero concentration) to the desired exposure concentration preceding the exposure period, and then drops off from the predetermined exposure concentration back to zero following the exposure time.
For situations where the “D” value is defined in minutes and hours, the effect of the transient periods of the BIER vessel cycle does not create significant errors in the overall measurement of the “D” value. However, in situations where a strong sterilant or a weak biological indicator is used, the “D” value may be relatively short, and in some cases, fractions of a second. In these cases, the effects of the “transient portion” of the BIER vessel operating cycle can create significant errors in the “D” value measurement. For sterilants that have low “D” values, or for relatively weak biological indicators, the transient portion of the operating cycle must be minimized or eliminated.
The present invention overcomes this and other problems and provides a BIER vessel system capable of exposing biological indicators to relatively short exposure periods.